1. Field of the Invention
This invention relates to the field of three-dimensional displays.
1. Prior Art
Traditional refractive optics has produced two screen-like mechanisms for three-dimensional viewing without headgear. The first screen mechanism is the Fresnel screen. This technique utilizes twin images projected onto a Fresnel lens, as if it were a projection screen. In a typical situation, the view is as far in front of the lens as the projectors are behind it. If the projectors are spaced the same as the viewer's eyes, then the viewer can be positioned so that each eye receives the appropriate image, and stereo vision results. Unfortunately, this process is limited by size of the system's exit pupil, and only one viewer is possible, since his head will fill the exit pupil. Also, to avoid loss of viewing, the viewer's movement must be restricted.
The second screen mechanism uses lenticular plates in the form of sheets consisting of hundreds or thousands of narrow cylinder lenses arrayed in parallel, and produces some important improvements. In essence, the Fresnel screen of the first system is replaced by a sandwich of diffusing medium between two lenticular plates. The lenticules face outward and run vertically. Lenticules on the two plates are carefully aligned to be parallel to and in line with each other. Again, the twin images are projected onto the screen. In this case however, each lenticule on the first sheet images the strip of image falling on it onto the diffusing material. The lenticules of the second sheet then allow viewing of each total image only from particular angles. Because of the diffusion material and arrangement of lenticules, the vertical axis of the exit pupil is extended. Also, as lenticules in the second sheet image strips not only in line, but perhaps one or two strips adjacent, multiple exit pupils are created, allowing multiple viewers. An additional advantage of the lenticular screen is that a multiplicity of images projected onto the screen will be presented to the viewer as a continuous, autostereoscopic field. This permits the viewer to move within the field and to perceive motion parallax. A disadvantage to this technique, however, is the difficulty of manufacturing large lenticular sheets and performing the careful alignment needed to assemble the screen.
The present invention preserves the advantages of a continuous autostereoscopic field for motion parallax and multiple viewer capabilities, but does so in a much more easily and inexpensively manufactured system.